Flotation plant

ABSTRACT

In a flotation plant comprising an intake installation (1), a flocculation section (2), a separating section (4), a water discharge installation (5), a sedimentation section, a slurry collecting section (7), a scraper (8) for the slurry, a trough (9) for the slurry, and pushers (10) for conveying the same, a laminating section (3) is incorporated between the flocculation section (2) and the slurry collecting section (7). The laminating section (3) is composed of a plurality of equiaxial divergent circular-section members arranged to form, on the one hand, mutually equal base areas and, on the other hand, mutually equal exit areas of the respective annuli. Both the flocculating section (2) and the laminating section (3) are positioned centrally inside a cistern (4, 6) of the flotation plant.

The present invention relates to a flotation plant, particularly fortreating waste waters, which comprises an intake installation, aflocculation section, a laminating section composed of a plurality ofequiaxial divergent circular-section members, a separating section, awater discharge installation, a sedimentation section, a slurrycollecting section, a scraper for the slurry, a trough for the slurryand pushers for conveying the same.

In patent U.S. Pat. No. 4,931,175 to Krofta a Water Clarifying Apparatusis disclosed having a cylindrical tank where particulate contaminantssuspended in raw water are separated using flotation techniques. A setof concentric mutually spaced, conical plates are positioned in theflotation tank. The plates rotate about the tank, preferably in unisonwith (i) a header that distributes equal quantities of raw water to eachannular zone in the tank defined by the conical plates and (ii) a scoopfor removing the contaminants which form a floated sludge layer.

It is a drawback of the known apparatus that the plates constituting alaminating section, i.e. a main section of the apparatus, rotate.Namely, the rotating assembly is submersed; no approach is possible inorder to maintain e.g. the bearings, which means that special bearingsor special lubricating arrangements are required.

Besides, the known apparatus operates by the decompressing of airdissolved in water. To this end, a portion of clarified water must bereturned into the process. Approximately 30 to 40% of the capacity ofthe apparatus is involved thereby, which results in respective reductionof the efficiency and increase of energy consumption.

It is an object of the present invention to avoid the disadvantages ofthe prior art and to provide a flotation plant creating a uniform flowpattern of a fluid through all its passages in a continuous operation,preferably a laminar flow pattern of the fluid downstream from theintake chamber of the plant.

According to this invention, a laminar flow pattern is obtainable underthe following conditions.

The laminating section is arranged to form, on the one hand, mutuallyequal base areas and, on the other hand, mutually equal exit areas ofthe respective annuli.

The exit areas of the laminating section are 1.4 times larger than thebase ones.

The base i.e. intake areas of the annuli of the laminating section allreside in a horizontal plane, and the upper i.e. exit areas of theannuli of the laminating section are arranged to form a hemisphere.

The laminating section is supported by an intake vessel. The intakevessel of the flocculating section and the outer divergent member of thelaminating section form a uniform divergent member.

A bottom member of the intake vessel and a bottom member of a flotationcistern are integral and arranged in a common horizontal plane.

The total exit area of the laminating section equals the mantle surfaceof a virtual cylinder defined by the largest diameter of the laminatingsection and by the height clearance between the laminating section atthe location of the said largest diameter and the upper edge of thecistern.

The total exit area of the laminating section also equals an intake gapof an annulus in the horizontal plane between the laminating section andthe cistern.

The cistern provides an upper, cylindrical part and a lower,funnel-shaped part with the connection site between the said two partsbeing located at a level approximately corresponding to a half of theheight of the flocculating section.

A horizontal annulus area at the location corresponding to theconnection site of the cylindrical part and the funnel-shaped part ofthe cistern is 1.5 times larger than the horizontal annulus area of theintake gap existing between the laminating section and the cistern.

In the height region approximately corresponding to the connection sitebetween the two parts of the cistern, a floccule-free water dischargecollecting installation is arranged, which is composed of a torus-typetube arranged around the cistern, said tube being connected by radialdischarge tube arms at mutually equidistantly arranged locations to therespective annulus of the cistern.

Hereinafter, the invention is disclosed in detail by means of anillustrative embodiment shown in the drawing. In the drawing:

FIG. 1. is an elevational axial section of the flotation plant of theinvention,

FIG. 2. is an elevational sideview of the flotation plant of FIG. 1, and

FIG. 3 is an elevational axial section of the intake installation.

The flotation treatment starts in an upright intake vessel where aflocculating section 2 of the flotation plant is created. Basically, thesaid vessel is circular in its cross section and divergent in its axialdirection.

A bottom member of the said vessel, preferably integral with a bottommember of a flotation cistern 4, 6, accommodates an intake installation1 (FIG. 3), which, according to the invention, is a special supplyingassembly comprising an outer tube--for supplying waste water including aflocculating agent being added prior to entering the vessel--and aninner self-suction dispersing nozzle i.e. a special device which bymeans of a forcing central water stream sucks the air conveyed through acoaxial outer tube.

The said self-suction dispersing nozzle is the object of a parallelpatent SI 9600143 and a respective patent application WO 97/41962(PCT/SI97/00014) here considered as a reference.

The said supplying assembly evidently creates two annuli--one for wastewater and one for air--and a central tube (for the forcing water).

Waste water enters the said flocculating section 2 in the form of avertical flow dispersed radially under an angle of e.g. 45°. Thereafter,it is crossed by a strong horizontal radial stream of an air-waterdispersion created in the said self-suction dispersing nozzle. In theflocculating section 2, waste water is intensively mixed with airbubbles. Floccules are created, to which the bubbles generating thelifting power of the particles adhere.

According to the invention, the said intake vessel supports asuperstructure to form a laminating section 3.

The laminating section 3 is composed of a plurality of equiaxialdivergent circular-section members arranged to form mutually equal baseareas of the respective annuli. The same applies to the exit areas ofthe said annuli, the exit areas being 1.4 times larger than the baseones.

The outer one of the said divergent members is preferably integral withthe vessel of the underlying flocculating section 2, most preferablydesigned to form a uniform divergent member.

The base (intake) areas of the annuli of the laminating section 3 allreside in a horizontal plane. In contrast, the upper (exit) areas of theannuli of the laminating section 3 are preferably arranged to form ahemisphere.

Both the flocculating section 2 and the laminating section 3 arepositioned centrally inside the cistern 4, 6 of the flotation plant.

The upper edge of the cistern 4 resides at a higher level than the upperedge of the inner divergent member of the laminating section 3 so thatover the laminating section 3 a slurry collecting section 7 of theflotation plant is created.

The total exit area of the laminating section 3 equals the mantlesurface of a virtual cylinder defined by the largest diameter of thelaminating section 3 and by the height clearance between the laminatingsection 3 at the location of the said largest diameter and the upperedge of the cistern 4. The same flowing area is also provided in thehorizontal plane by the intake gap of the annulus between the laminatingsection 3 and the cistern 4.

The cistern 4, 6 is--in addition to the bottom member alreadymentioned--suitably composed of an upper, cylindrical part 4 and alower, funnel-shaped part 6. The connection site between the said twoparts 4, 6 is suitably located at a level corresponding to a half of theheight of the flocculating section 2. The region of the cistern insidethe cylindrical part 4 is foreseen to definitely separate water fromfloccules and to eventually collect water free of floccules, and theregion of the cistern inside the funnel-shaped part 6 is foreseen tocollect the sediment. To this end, in the region of the connection siteof the cylindrical and the funnel-shaped parts 4, 6 of the cistern adischarge collecting installation 5 is arranged, and in the bottommember of the cistern outlets for a temporary removing of the sedimentare arranged.

The discharge collecting installation 5 is composed of a torus-type tubearranged around the cistern of the flotation plant, the said tube beingconnected by radial discharge tube arms at (eight) mutuallyequidistantly arranged locations to the floccule-free water compartment.

By means of an intermediate funnel-shaped member arranged in the saidseparating and floccule-free water compartment in the height regionbelow the largest diameter of the laminating section 3 and supported bythe said radial discharge tube arms, the floccule-free water compartmentof the cistern 4 is divided into two annuli.

The lower area of the separating and floccule-free water compartment ofthe cistern is suitably 1.5 times larger than the upper, intake one.Such a design results in reducing the vertical velocity of the fluid,which contributes to the separation effect.

A slurry collecting section 7 is the upper section of the plant over thelaminating section 3 and the separating annulus, which provides thecollecting and draining of the slurry. The layer of slurry thickens andgets thicker from the centre to the periphery of the cistern. In themiddle and at the periphery the respective thicknesses of the slurrylayer amount to approximately 5 cm and 25 cm.

A scraper 8 for scraping the slurry is designed as a cross member havingdoctor blades attached thereto. The angle formed by a doctor blade and atangent to the circular periphery of the cistern is adjustable. Therebythe intensity of removing the slurry can be controlled. The doctorblades are inclined under an angle of 45° in the direction of cuttingthe slurry. Along the edge of the slurry collecting section 7, where thethickness of slurry is the highest, the slurry is displaced by doctorblades into a trough 9.

A horizontal trough 9 is arranged along the periphery of the slurrycollecting section 7. The trough 9 provides a funnel-shaped dischargemember (FIG. 2) with an adapter to connect a slurry pump, arranged atthe bottom thereof.

Each of the four arms of the scraper 8 supports a pusher memberpositioned inside the trough 9 for pushing the slurry along the trough 9up to the discharge member thereof.

The flotation plant functions as follows.

A turbulent flow of floccules and waste water of the flocculatingsection 2 is converted into laminar sub-flows in the laminating section3. Volume flows through individual annuli are mutually equal and theyadd up in radial direction at the exit site of the laminating section 3.A constant flow velocity of the fluid in radial direction is obtainableby the upper hemispherical surface of the laminating section 3. The flowvelocity of the fluid is constant downstream from the laminating section3 through the slurry collecting section 7 up to the intake into theseparating section. Along the separating section the flow velocitydecreases.

What is claimed is:
 1. A flotation device comprising a flotation tankhaving a bottom wall and a side wall an intake installation (1) forfeeding waste water and air into a lower portion of the tank, meansdefining a flocculation section (2) which comprises a generally opentopped cone shaped member, a laminating section (3) at the top of theflocculation section (2) which comprises a plurality of equiaxialdivergent circular-section members, said side wall of the flotation tankextending over said laminating section (3) for collecting a slurry abovesaid laminating section (3) and below a scraper (8), a separatingsection (4) provided with a water discharge installation (5) arrangedadjacent a bottom section of said side wall of the flotation tank, and asedimentation section provided at the bottom of said separating section(4), wherein said laminating section (3) is arranged to form, on the onehand, mutually equal base areas and, on the other hand, mutually equalexit areas of the respective annuli.
 2. Flotation device as in claim 1,wherein the exit areas of said laminating section (3) are 1.4 timeslarger than the base areas.
 3. Flotation device as in claim 1, whereinsaid base areas are intake areas and wherein said base areas of theannuli of the laminating section (3) all reside in a horizontal plane,and the upper, i.e. exit areas of the annuli of the laminating section(3) are arranged to form a hemisphere.
 4. Flotation device as in claim1, wherein said laminating section (3) is supported by said bottom wallof the flotation tank.
 5. Flotation device as in claim 4, wherein saidmeans defining the flocculating section (2) and the outer divergentmember of the laminating section (3) form a uniform divergent member. 6.Flotation device as in claim 4 wherein said means defining theflocculation section (2) includes a bottom member, said bottom memberand said bottom wall of the flotation tank are integral and are arrangedin a common horizontal plane.
 7. Flotation device as in claim 6, whereinthe total exit area of said laminating section (3) i.e. the sum of itshorizontal exit orifice areas of the annuli and a central orifice areaequals a mantle surface (S=π×D×H; π=3.14) of an imaginary cylinderdefined by a largest diameter (D) of the laminating section (3) and aheight clearance (H) between said laminating section (3) (at thelocation of said largest diameter) and the upper edge of said side wallof the flotation tank.
 8. Flotation device as in claim 6, wherein thetotal exit area of said laminating section (3) equals an intake gap ofan annulus in the horizontal plane between said laminating section (3)and said side wall of the flotation tank.
 9. Flotation device as inclaim 6, wherein said side wall of the flotation tank is generallycylindrical and said bottom wall provides a funnel-shaped part with theconnection site between said two walls of the flotation tank beinglocated at a level approximately corresponding to a half of the heightof said flocculating section (2).
 10. Flotation device as in claim 8,wherein a horizontal annulus area at the location corresponding to theconnection site of the cylindrical part of said side wall of theflotation tank and the funnel-shaped part of said bottom wall of theflotation tank is approximately 1.5 times larger than the horizontalannulus area of the intake gap between said laminating section (3) andsaid side wall of the flotation tank.
 11. Flotation device as in claim9, wherein the height region approximately corresponding to theconnection site between the bottom wall and the side wall of theflotation tank, said water discharge installation (5) is a floccule-freewater discharge collection installation and comprises a torus-type tubearranged around said flotation tank, said tube being connected by radialdischarge tube arms at mutually equidistantly arranged locations to therespective annulus of said flotation tank.